1. Field of the Invention
The present invention relates to a semiconductor device process, more specifically, to a method for detecting if there is any void in STI.
2. Description of the Prior Art
In the process for semiconductor devices getting more and more compact, shallow trench isolation (STI) is used to separate active areas 10 for forming respective elements. STI is formed between active areas 10 and is filled with dielectric 12, which can be oxide such as silicon oxide. However, a void 13 is likely to be generated in the step of filling with the dielectric 12, as shown in FIG. 1.
In DRAM process, such a condition also happens. With reference to FIG. 2, which is a schematic top view of a gate region structure of a DRAM, reference number 20 indicates an active area, 21 indicates a gate line, 24 indicates a deep trench. As shown in the drawing, the adjacent portion between the active areas is short. Reference number 23 indicates a void formed in the dielectric filled in the STI between the active areas 20. The existence of the void 23 may influence the electric performance of the semiconductor structure. However, such a void is very small and is hardly found during the process. Usually, the existence of the void only can be found in the electric testing, for example, testing of voltage (potential, current, resistance, inductance, or capacitance between two gate lines 21, which is performed after the wafer is finished, cut into chips and packed. Accordingly, a waste of process is generated.
Therefore, there is a need for a solution to overcome the problems stated above. The present invention satisfies such a need.